Producing all skin rayon



United PRODUCING ALL SKIN RAYON No Drawing. Application December 5, 1955 Serial No. 550,839

3 Claims. (Cl. 106-465) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable celulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two.

The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and providing that the amount of adduct is maintained within certain limits and the composition of the spinning bath is maintained within certain composition limits which will Patent F 2,919,203 Patented Dec. 29, 1959 "ice be defined hereinafter. The most readily distinguishable characteristic as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

This invention contemplates the use of such compounds which may be termed di(omega-hydroxy polyoxyalkylene)-ethyl N-morpholino amines as represented by the formula Hz-CH: (Calla-ONE where n is 2 or 3, x and y are whole numbers and the sum of x and y varies from 3 to or more. It is possible that the adducts may have hydroxy polyoxyalkylene chains of'diiferent length and that the alkylene oxide units are not in all cases equally distributed in the adducts. The alkylene oxide content of the adducts may be expressed as the average number of alkylene oxide units per molecule of B-aminoethyl morpholine. The adducts must have sufiicient water and alkali solubility to permit the required amount to be dissolved in the viscose, spinning bath or both. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and alkali solutions such as a 6% caustic soda solution, the ethylene oxide adducts are preferred although propylene oxide adducts are satisfactory. Accordingly, the invention will be illustrated specifically by reference to ethylene oxide adducts. I

The upper limit of the number of alkylene oxide units is determined by the solubility and stability characteristics of the adducts. Thus, the upper limit in the case of propylene oxide adduct is lower than the upper limit for the'ethylene oxide adducts. For practical and commercial purposes, it is uneconomic to employ adducts having alkylene oxide contents approaching the upper limit because these higher cost substances are not more effective than the lower and intermediate substances. Thus, in the case of the ethylene oxide adducts, it is preferred to employ adducts containing between about 5 and about 60 ethylene oxide units per molecule of B-aminoethyl morpholine. The production of all skin products requires that certain minimum and limited amounts of the adduct be in solution in the viscose. The adductor modifier may be conveniently added to the viscose in the form of a solution in alkali or in water.

The amount of the adduct which is incorporated in viscose must be at least about 0.75% by weight of the cellulose in the viscose and may vary up to about 3%, preferably, the amount varies from about 1% to 2%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The

adduct may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The adduct is preferably added after the cellulose xanthate has been dissolved in the caustic solution selected for the ultimate use of the regenerated cellulose The caustic soda content may be from about product. 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight 2,919,2os Y of the cellulose. The modified viscose, that is, a viscose containing the small amount of alkylene oxide adduct of B-aminoethyl morpholine, may have a sodium chloride salt test above about 8 and preferably above about 9 at the time of spinning or extrusion.

' In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of these adducts in the viscose combined with these limited spinning baths results in the produc tion of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically, and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about 10% to about 25% sodium sulfate and from about 3% to about 15% zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 6., preferably between about 45 C. and about 70 C. The temperature is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is 'sufiiciently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufficiently rapid to produce filaments having a skin and core. For example, in general, the acid con-- centration of the spinning baths which are satisfactory for the production of the all skin products from a 7% cellulose, 6% caustic-viscose and containing these adducts lies between about and about 8%. Lesser amounts of acid may be employed. The acid concentration may be increased as the amount of the adduct is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of adduct and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of adduct is increased beyond about 3% while other conditions are maintained constant. A lowering of the amount of the adduct in the viscose, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. The maximum concentration of acid which is permissible for the production of all skin products in accordance with this invention is about 9%.

The presence of the alkylene oxide adducts in the viscose retards the coagulation and, therefore, the amount of adduct employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the adduct is employed in amounts within the lower portion of the range, for example, about 1%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufficient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufficient sothat the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to 120%, preferably between 75% and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed throught a final regenerating bath which may contain from about 1% to about5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the adducts and spun in the spinning baths of limited acid content have a smooth or noncrenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the adducts have superior abrasion and fatigue resistance characteristics and have a high flex-life as compared to normal regenerated cellulose filaments. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7.4% cellulose, about 6.6% caustic soda, and having a total carbon disulfide content of about 36% based on the weight of the cellulose. The viscose solutions were prepared by xa'nthating alkali cellulose by the introduction cf 36% carbon disulfide based on the weight of the cellulose and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The viscose was then allowed to ripen for about 28 hours at 18 C. In those instances where an ethylene oxide adduct was incorporated in the viscose, the desired amount of an adduct containing 50 ethylene oxide units per molecule of B-aminoethyl morpholine was added to the solution and mixed for about /2 hour before allowing the viscose to ripen. The compound may be considered as having a formula as set forth in column 2 where n is 2 and x plus y is 50, x and y may be considered as being 25.

In each instance, the viscose was extruded through a spinneret to form a 200 to 210 denier, 100 filament yarn at the rate set forth in the table which follows. The coagulating and regenerating bath was maintained at a temperature of about 60 C. The yarn after removal from the spinning bath was passed through a hot water bath maintained at about 95 C. and was stretched while passing through this bath. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The specific spinning conditions and the physical properties of the yarns are set forth in the following table:

Example I II III IV V VI VII Viscose:

Percent Adduct 1 1 2 0 2 0 Salt Test 9. 9. 5 9. 7 9. 3 9.8 10. 8 10. 6 Bath:

Percent H1804 7.7 7. 6 7. 7 7.8 7. 7 8. 7 8. 7 Percent ZHSOL. 5 5 6 7 6 6 6 Percent NazSO 18 17 l5 I5 l6 l6 Spin Speed 22 22 22 22 22 36 36 Percent Stretch. 82 82 82 82 82 76 76 Spin speed-Speed of extrusion of viscose in meters per minute. T. dry and '1. wet-Tensile strength of dry and wet yarn, respectively, in grams per denier.

dry and E. wetPercent elongation of dry and wet yarn, respecl iaiisile strengths and percent elongation not. determined for Examples VI and VII.

The individual filaments formed in accordance with this invention have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e.g. l500 The filaments of the control yarns (Examples II, V and VII) formed from the same viscose solutions and spun under the same conditions but without the adduct or modifier of the type described exhibit a very irregular and serrated surface and are composed of about 50% to 60% skin and the balance core with a sharp line of demarkation between the skin and core.

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tenacity and elongation, however, the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, fiex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

If desired, small amounts of the ether may be added to the spinning bath. Since the ethers are water-soluble, some of the ether will be leached from the filament or other shaped body and will be present in the bath.

The alkylene oxide adducts may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The adduct may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyer's albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for l to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A viscose spinning solution containing from about 4% to about 10% cellulose and from about 0.75% to about 3%, based on the weight of the cellulose in the viscose, of a di(omega-hydroxy polyoxyalkylene)-ethyl N-morpholino amine wherein the alkylene oxide is selected from the group consisting of ethylene oxide and propylene oxide and the amine contains between about 3 to about alkylene oxide units.

2. A viscose spinning solution as defined in claim 1 wherein the alkylene oxide in the amine is ethylene oxide.

3. A viscose spinning solution containing a small amount of a di(omega-hydroxy polyoxyalkylene)-ethyl N-morpholino amine wherein the alkylene oxide is selected from the group consisting of ethylene oxide and propylene oxide and the amine contains between about 3 and about 100 alkylene oxide units, said small amount of the amine being a quantity sufiicient to impart a smooth, non-crenulated surface and a substantially all skin structure to products formed by spinning the viscose at a sodium chloride salt test of at least 8 into an aqueous bath containing from 15% to 22% sodium sulfate, from 4% to 9% zinc sulfate and sulfuric acid in an amount not exceeding 9%, but the quantity being insufiicient to adversely affect the physical properties of such products.

References Cited in the file of this patent UNITED STATES PATENTS 2,495,833 Brown Jan. 31, 1950 2,535,044 Cox Dec. 26, 1950 2,593,466 MacLaurin Apr. 22, 1952 2,648,611 Richter Aug. 11, 1953 2,705,184 Drisch Mar. 29, 1955 2,732,279 Tachikawa Jan. 24, 1956 2,784,107 Tallis et al Mar. 5, 1957 2,792,279 Lytton May 14, 1957 2,805,169 Mitchell Sept. 3, 1957 

1. A VISCOSE SPINNING SOLUTION CONTAINING FROM ABOUT 4% TO ABOUT 10% CELLULOSE SND FROM ABOUT 0.75% TO ABOUT 3%, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, OF A DI(OMEGA-HYDROXY POLYOXYALKYLENE) -ETHYL N-MORPHOLINO AMINE WHEREIN THE ALKYLENE OXIDE IS SELECTED FROM THE AMINE CONTAINS BETWEEN ABOUT 3 TO ABOUT 100 ALKYLENE OXIDE UNITS. 